Cadillac 2006 DTS Owner's Manual page 338

The battery is located under the rear seat cushion. To
access the battery, see Rear Underseat Fuse Block on
page 5-96. You do not need to access the battery to jump
start your vehicle. See Jump Starting on page 5-39.
CAUTION:
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A battery that is not properly vented can let
sulfuric acid fumes into the area under the rear
seat cushion. These fumes can damage your
rear seat safety belt systems. You may not be
able to see this damage, and the safety belts
might not provide the protection needed in a
crash. If a replacement battery is ever needed,
it must be vented in the same manner as the
original battery. Always make sure that the
vent hose is properly reattached before
reinstalling the seat cushion.
5-38
To be sure the vent hose (A) is properly attached, the
vent hose connectors (B) must be securely reattached to
the vent outlets (C) on each side of the battery, and
the vent assembly grommet (D) must be secured to the
floor pan (E).